The project deals with fibronectin (LETS protein), a cell surface glycoprotein found in fibroblasts and other cells. Fibronectin is a high molecular weight glycoprotein and it is present on the surface of normal, but not of malignant cells. The malignant cells do produce fibronectin, but it is not retained on their surface like it is in normal cells. Recent studies show that fibronectin binds to collagen. Fibronectin will be isolated from various sources (normal fibroblasts, spent medium of normal and transformed fibroblasts, plasma) and characterized and compared biochemically and with respect to the collagen-binding properties. Antibodies will be used to study the structure of the fibronectin molecule and its orientation on the cell surface. Attempts to work out the specificity of the fibronectin binding site(s) to collagen and cell surfaces will be made. Purified fibronectin, its fragments and anti-fibronectin antibodies will be used in cell cultures in attempts to define the role of fibronectin in growth control.